1. Field of the Disclosure
The present subject matter relates to a bearing and bearing assembly for supporting an umbilicus used, for example, in a fluid processing system.
2. Description of Related Art
Whole blood is routinely separated into its various components, such as red blood cells, platelets, and plasma. In typical blood processing systems, whole blood is drawn from a donor, the particular blood component or constituent is removed and collected, and the remaining blood constituents are returned to the donor. By thus removing only particular constituents, less time is needed for the donor's body to return to normal, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for health care.
Whole blood is typically separated into its constituents through centrifugation. This requires that the whole blood be passed through a centrifuge after it is withdrawn from, and before it is returned to, the donor. To avoid contamination, the blood is usually contained within a sealed, sterile system during the entire centrifugation process. Typical blood processing systems thus include a permanent, reusable centrifuge assembly or “hardware” that spins and pumps the blood, and a disposable, sealed and sterile fluid processing or fluid circuit assembly that actually makes contact with the donor's blood. The centrifuge assembly engages and spins a portion of the fluid processing assembly (often called the centrifuge or separation chamber) during a collection procedure. The blood, however, makes actual contact only with the fluid processing assembly, which is used only once and then discarded.
To avoid the need for rotating seals, and to preserve the sterile and sealed integrity of the fluid processing assembly, blood processing systems often utilize centrifuges that operate on the “one-omega, two-omega” operating principle. This principle is disclosed in detail in U.S. Pat. No. 4,120,449 to Brown et al., which is hereby incorporated by reference, and enables centrifuges to spin a sealed, closed system without the need for rotating seals and without twisting the components of the system. Blood processing systems that make use of the principle typically include a fluid processing assembly that includes a plastic bag or molded chamber that is spun in the centrifuge and that is connected to the blood donor and to a stationary portion of the centrifuge assembly through an elongated member that may be made up of one or more plastic tubes. The elongated member is commonly referred to as an “umbilicus” and is typically arranged in a question mark (or upside-down question mark) configuration with both of its end portions coaxially aligned with the axis of rotation of the centrifuge. The centrifuge chamber is rotated at “two-omega” RPM and the umbilicus is orbited around the centrifuge chamber at “one-omega” RPM. In other words, one end of the umbilicus is stationary, the other end rotates at a two-omega speed with the centrifuge chamber to which it is attached, and the intermediate portion or midsection of the umbilicus orbits about the chamber at a one-omega speed. The effect is that the end of the umbilicus, which is opposite the bag or chamber and is connected to the donor via plastic tubing, does not twist up as the bag is spun. The sealed, sterile integrity of the fluid processing assembly is thus maintained without the need for rotating seals.
U.S. Pat. Nos. 5,989,177 to West et al. and 6,344,020 to Reitz et al., both of which are hereby incorporated herein by reference, disclose one such blood processing apparatus based on the “one-omega, two-omega” operating principle. In this apparatus, a disposable fluid processing assembly having an umbilicus and a processing chamber is mountable within a centrifuge assembly. One end of the umbilicus is held rotationally stationary substantially coaxial with the axis of centrifugal rotation. The other end of the umbilicus joins the processing chamber and rotates with the processing chamber around the axis of centrifugation at the two-omega speed, up to about 3,000 RPM. The mid-portion of the umbilicus is supported by a wing plate that rotates around the axis of centrifugation at the one-omega speed, up to about 1,500 RPM. A thrust bearing mounted on the umbilicus permits the umbilicus to rotate relative to the wing plate as the wing plate and the processing chamber turn at different speeds. The thrust bearing slides into a one piece gimbal mounted in a recess provided on the wing plate. The gimbal helps keep the fluid processing assembly properly positioned during the centrifugation procedure. When the procedure is completed, the thrust bearing can be slid out of the gimbal in the wing plate to permit removal of the fluid processing assembly.
Prior thrust bearings employ a plurality of ball bearings to facilitate relative rotation between the umbilicus and wing plate. While such systems have proven suitable, they require a number of precision components to accommodate the ball bearings, and there remains a need for an improved and preferably lower cost bearing or bearing assembly for such processing systems, particularly that don't employ ball bearing arrangements.